Scavenging hydrogen sulfide

ABSTRACT

Alpha-hydroxy alkyl esters have been found to perform as hydrogen sulfide scavengers. A method of scavenging hydrogen sulfide includes contacting a fluid containing hydrogen sulfide with a treatment fluid including an alpha-hydroxy alkyl ester. Accordingly, the alpha-hydroxy alkyl ester reacts with the hydrogen sulfide to reduce the amount of hydrogen sulfide in the fluid. A broad range of alpha-hydroxy alkyl esters are disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 61/739,390, filed on Dec. 19, 2012.

BACKGROUND

Field of the Invention

The present invention relates to a process of scavenging hydrogensulfide from a fluid.

Background of the Related Art

Production fluids that are produced from subterranean formation willoften contain hydrogen sulfide (H₂S). Production fluids that include ahigh concentration of hydrogen sulfide are sometimes referred to asbeing “sour” and those production fluids that include little or nohydrogen sulfide are sometimes referred to as being “sweet.” Hydrogensulfide is a toxic and pungent gas and, because it behaves as a weakacid in water, can cause corrosion of steel equipment and pipelines.Natural gas must ordinarily contain less than 4 parts per million (ppm)of hydrogen sulfide before it can be sold. Accordingly, productionfluids may be “sweetened” through a process of removing the hydrogensulfide. Typical hydrogen sulfide removal processes use an activetreatment compound that reacts with the hydrogen sulfide.

Common sweetening processes pass the already produced production fluidsthrough equipment where the hydrogen sulfide is contacted with an activetreatment compound referred to as a “hydrogen sulfide scavenger” or,more simply, a “scavenger.” The hydrogen sulfide scavenger reacts withthe toxic hydrogen sulfide to form a nontoxic compound. Liquidscavengers, for example, may be injected into a pipeline or processingequipment

BRIEF SUMMARY

The present invention provides a method of scavenging hydrogen sulfide.The method comprises contacting a fluid containing hydrogen sulfide witha treatment fluid including at least one reaction product of a firstcompound with at least one carboxylic acid group and a second compoundwith at least one aldehyde group, wherein the hydrogen sulfide reactswith the said reaction product to reduce an amount of the hydrogensulfide in the production fluid. In one example, the reaction productincludes an alpha-hydroxy alkyl ester.

DETAILED DESCRIPTION

The present invention provides a method of scavenging hydrogen sulfide.The method comprises contacting a fluid containing hydrogen sulfide witha treatment fluid including at least one reaction product of a firstcompound with at least one carboxylic acid group and a second compoundwith at least one aldehyde group, wherein the hydrogen sulfide reactswith the said reaction product to reduce an amount of the hydrogensulfide in the production fluid. In one example, the reaction productincludes an alpha-hydroxy alkyl ester.

The method may use any one or more of a broad range of alpha-hydroxyalkyl esters. One embodiment of the alpha-hydroxy alkyl ester is thereaction product of a carboxylic acid and an aldehyde. Optionally, thecarboxylic acid may be a mono carboxylic acid, dicarboxylic acid,oligomeric carboxylic acid, or polymeric carboxylic acid. Independently,the carboxylic acid and/or the aldehyde may be saturated, unsaturated oraromatic. The alpha-hydroxy alkyl ester may also be amine-free.

Another embodiment of the alpha-hydroxy alkyl ester has no nitrogen orbasic nitrogen (amine functionalities). In a still further embodiment,the alpha-hydroxy alkyl ester is functionalized with a phosphate group,phosphonate group, sulfate group, sulfonate group, or hydroxyl group. Ina first option, the alpha-hydroxy alkyl ester includes two phosphategroups or two sulfate groups. In a second option, the alpha-hydroxyalkyl ester includes at least two hydroxyl groups.

In a still further embodiment, the alpha-hydroxy alkyl ester is areaction product of a mono-carboxylic acid, dicarboxylic acid,oligomeric carboxylic acid, or polymeric carboxylic acid reacted with amono-aldehyde, dialdehyde, oligomeric aldehyde, or polymeric aldehyde.Accordingly, the reaction products may include a polyester, a cyclicdi-ester, or some mixtures thereof.

Specific examples of alpha-hydroxy alkyl esters that may be used in themethods of the present invention include, without limitation,bis(hydroxymethyl) Maleate; (2E, 4E)-hydroxymethyl hexa-2,4-dienoate;(E)-hydroxymethyl but-2-enoate; (E)-bis(hydroxymethyl)O,O′-(2-hydroxypropane-1,3-diyl) difumarate; hydroxymethyl6-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)hexanoate; sorbic acid, andcombinations thereof.

Embodiments of the invention may use a treatment fluid that includesbetween 5 and 20 volume percent of the alpha-hydroxy alkyl ester, orbetween 10 and 15 volume percent of the alpha-hydroxy alkyl ester.Optionally, the treatment fluid may further include a mixture of waterand ethanol, such as a 50/50 mixture of water and ethanol.

The fluid containing hydrogen sulfide may be any gas or liquid thatcontains hydrogen sulfide. The method is particularly useful to treatfluids that have been produced from a subterranean formation, but mayalso be used to treat industrial waste streams. In one example, thefluid containing hydrogen sulfide is a gas, such that the contactbetween the fluid containing hydrogen sulfide and the treatment fluidmay occur in an absorption tower.

In yet another embodiment, an alpha-hydroxy alkyl ester is included in asqueeze treatment. A “squeeze treatment” is a process of delivering atreatment fluid into a treatment zone of a subterranean formation bypumping the treatment fluid downhole under pressure, then shutting inthe treatment fluid for a period of time, such as between 12 and 16hours or longer, to allow the alpha-hydroxy alkyl ester to absorb ontothe surfaces of the formation before producing additional productionfluids. A squeeze treatment may, in accordance with the presentinvention, use a treatment fluid that includes one or more alpha-hydroxyalkyl esters. For example, a treatment fluid that includes one or morealpha-hydroxy alkyl esters may be pumped under pressure through awellbore into a subterranean formation, wherein the alpha-hydroxy alkylester adsorbs onto the subterranean formation in a region around thewellbore. Then, as production fluids subsequently flow from thesubterranean formation into the wellbore, the hydrogen sulfide reactswith the alpha-hydroxy alkyl ester as the production fluids flow throughthe region around the wellbore. Accordingly, an amount of hydrogensulfide in the production fluids is reduced before the production fluidsflow into the wellbore.

An alpha-hydroxy alkyl ester and other reaction products of carboxylicacids and aldehydes selected for use in a squeeze treatment willpreferably exhibit rock-surface adsorption, sulfide/mercaptan scavengingproperties, and compatibility with high brine fluids both before andafter the treatment compound reacts with sulfide/mercaptan species.These reaction products are also expected to not have scale issues thatare known for traditional triazines and other amine-containing hydrogensulfide scavengers.

After the alpha-hydroxy alkyl ester has been introduced into theformation, the compound absorbs onto the surfaces of the subterraneanrock formation. The desired adsorption is provided by the chemicalfunctionalities within the molecular structure of the alpha-hydroxyalkyl ester. It is believed that the oxygenation provided by the esterfunctionality, as well as other hydroxyl, phosphate and sulfate groups,provides the treatment compound with the ability to adsorb onto thesurface of the formation.

After the treatment compound has been introduced into the formation andadsorbed on the surface of the formation, the pressure in the well isreduced to allow formation fluids to be produced from the formation andup through the well. Typical formation fluids will include connate wateror brine in a mixture with liquid or gaseous hydrocarbons that containsulfur-containing compounds, such as hydrogen sulfide or mercaptans. Asthose formation fluids flow through the formation toward the well, theadsorbed alpha-hydroxy alkyl ester will come into contact with, andreact with, the sulfur-containing compounds. It should be appreciatedthat having the alpha-hydroxy alkyl ester adsorbed on the surface of theformation will increase the contact time with formation fluids, therebyincreasing the likelihood of reacting with more of the sulfur-containingcompounds.

Although a squeeze treatment in accordance with the present inventionmay be formulated and performed solely to deliver the alpha-hydroxyalkyl ester into the formation, a squeeze treatment may also includeother compositions that provide other beneficial effects. In anon-limiting example, the squeeze treatment may further include anadditive selected from a scale inhibitor, asphaltene inhibitor, abiocide, or some combination of the additives.

Alpha-Hydroxy Alkyl Esters

Although a number of alpha-hydroxy alkyl esters have been identifiedabove, the structures of these and other non-limiting examples ofsuitable alpha-hydroxy alkyl esters are presented below.

Generic Structure:

where: R=aliphatic, cyclic, acyclic, saturated, olefinic, aromatic; andR′=H, aliphatic, cyclic, acyclic, saturated, olefinic, aromatic.Example Preparation:

SPECIFIC EXAMPLES

where: R=aliphatic, cyclic, acyclic, saturated, olefinic, aromatic;

R1=H, aliphatic, cyclic, acyclic, saturated, olefinic, aromatic;

A=—OH, —OPO₃M, —SO₃M, —PO₃M₂; —OSO₃M;

M=H or metal ion; and

n=between 2 and 100 (preferably between 5 and 50, and more preferablybetween 10 and 20).

Examples Example 1 Synthesis Procedure for Bis(Hydroxymethyl) Maleate

To a stirred solution of maleic acid (50 g) in ethanol (80 mL) heated to60° C. in a round bottom flask was added a catalytic amount of 45%Potassium hydroxide (0.8 g). Paraformaldehyde prills (32 g) were thenadded portion-wise to the stirred solution over a 45 minute period andallowed to react for 5 hours. The reaction mixture yielded an ethanolicsolution of maleate derivatives including the desired Bis(hydroxylmethyl) maleate.

Example 2 Performance of Hydrogen Sulfide Scavenging Compounds

The performance of various hydrogen sulfide scavenging compounds,including a number of alpha-hydroxy alkyl esters, was measured using adynamic testing apparatus. A cadmium chloride solution was prepared byadding 125 grams of CdCl₂×2.5H₂O to a small amount of water and dilutionto 1 liter. Next, a 0.01 molar concentration solution of HCl is madeusing 8.5 milliters of concentrated HCl diluted to 1 liter. A 0.1Niodine solution and 0.1N Na₂S₂O₃ solution were purchased for theiodiometric titrations along with a starch reagent.

A dynamic testing apparatus was used to perform a dynamic test asdescribed in ASTM-D5705. Accordingly, two sparging flasks were filledwith the CdCl₂ solution and 15 ml of the 0.01M HCl solution. The twoflasks were connected using ⅝″ ID tubing. One of the hydrogen sulfidescavenging compounds was then placed into an empty sparging flask, whichwas itself connected by tubing to the flasks containing the CdCl₂solutions. The system was then purged with nitrogen gas to displace anyhydrogen sulfide from the fluid medium. CdS production was indicated bythe formation of a yellow precipitate. A sour fluid sample was dosedwith the scavenger chemistry being screened, sealed and placed into aheated mixing oven to simulate heated agitation.

The scrubbed CdS from the flasks was removed once the hydrogen sulfidehad been completely purged and was placed into a beaker for titration. Amagnetic stir bead was added to the beaker and placed onto a stir plate.Iodine solution and starch were added until the mixture had changed tothe color of the iodine. Na₂S₂O₃ was then used to titrate the iodine/CdSmixture. The CdS mixture was then titrated until the solution turnedclear (endpoint). A calculation was used to determine the remaininghydrogen sulfide using the results from the titration. This procedureallowed for measurement of H₂S in the original fluid medium withoutinterference from the reaction product of the hydrogen sulfidescavenging compound and H₂S.

TABLE 1 Results of Performance Testing Hydrogen Sulfide Extent ofRemoved in Liquid Phase Reaction Scavenger Composition (%) (%) Glycerolbis-hemiformal 89 18 Bis hydroxylmethyl maleate 39 58 Triazine 76 31

Table 1 shows the efficacy of a hydrogen sulfide scavenging compound interms of the percent of H₂S removed and the percent extent of reaction.The percent of H₂S removed is related to the overall scavenging capacityof the chemical. A high percent of percent of H₂S removed is desired.The percent extent of reaction is calculated based on the ratio of thechemical's theoretical capacity versus the actual capacity. It isdesired to have a high percent extent of reaction indicating that thescavenger molecule is reacting preferentially with the sulfur species toa greater extent so as not to be wasted in the scavenging process.Depending upon the chemical application a more prolonged effect of H₂Smay be desired versus a fast acting scavenging agent.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,components and/or groups, but do not preclude the presence or additionof one or more other features, integers, steps, operations, elements,components, and/or groups thereof. The terms “preferably,” “preferred,”“prefer,” “optionally,” “may,” and similar terms are used to indicatethat an item, condition or step being referred to is an optional (notrequired) feature of the invention.

The corresponding structures, materials, acts, and equivalents of allmeans or steps plus function elements in the claims below are intendedto include any structure, material, or act for performing the functionin combination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but it is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

What is claimed is:
 1. A method of reducing the amount of hydrogensulfide in a hydrocarbon-containing fluid, the method comprising:contacting the hydrocarbon-containing fluid with a treatment fluidincluding at least one alpha-hydroxy alkyl ester, wherein the hydrogensulfide reacts with the alpha-hydroxy alkyl ester to reduce an amount ofthe hydrogen sulfide in the hydrocarbon-containing fluid; and whereinthe alpha-hydroxy alkyl ester is selected from the group consisting ofbis(hydroxymethyl) maleate; (2E, 4E)-hydroxymethyl hexa-2,4-dienoate;(E)-hydroxymethyl but-2-enoate; (E)-bis(hydroxymethyl)O,O′-(2-hydroxypropane-1,3-diyl) difumarate; hydroxymethyl6-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)hexanoate; and a combinationthereof.
 2. The method of claim 1, wherein the reaction product isamine-free.
 3. The method of claim 1, wherein the treatment fluidincludes between 5 and 20 volume percent of the alpha-hydroxy alkylester.
 4. The method of claim 1, wherein the treatment fluid includesbetween 10 and 15 volume percent of the alpha-hydroxy alkyl ester. 5.The method of claim 1, wherein the treatment fluid includes a mixture ofwater and ethanol.
 6. The method of claim 1, wherein thehydrocarbon-containing fluid has been produced from a subterraneanformation.
 7. The method of claim 6, wherein the hydrocarbon-containingfluid is a gas.
 8. The method of claim 7, wherein the contact betweenthe hydrocarbon-containing fluid and the treatment fluid occurs in anabsorption tower.
 9. The method of claim 1, wherein contacting thehydrocarbon-containing fluid with the treatment fluid including the atleast one alpha-hydroxy alkyl ester comprises: pumping the treatmentfluid under pressure through a wellbore into a subterranean formationand maintaining the treatment fluid in the region around the wellborefor a predetermined period of time, wherein the alpha-hydroxy alkylester adsorbs onto the subterranean formation in a region around thewellbore; and flowing the hydrocarbon-containing fluid from thesubterranean formation into the wellbore, wherein the hydrogen sulfidereacts with the alpha-hydroxy alkyl ester as the hydrocarbon-containingfluid flows through the region around the wellbore to reduce an amountof hydrogen sulfide in the hydrocarbon-containing fluid before thehydrocarbon-containing fluid flows into the wellbore.
 10. The method ofclaim 9, wherein the treatment fluid is maintained in the region aroundthe wellbore for a predetermined period of time to allow thealpha-hydroxy alkyl ester to absorb onto the subterranean formation. 11.The method of claim 1, wherein the alpha-hydroxy alkyl ester comprisesbis(hydroxymethyl) maleate.
 12. The method of claim 1, wherein thealpha-hydroxy alkyl ester comprises (2E, 4E)-hydroxymethylhexa-2,4-dienoate.
 13. The method of claim 1, wherein the alpha-hydroxyalkyl ester comprises (E)-hydroxymethyl but-2-enoate.
 14. The method ofclaim 1, wherein the alpha-hydroxy alkyl ester comprises(E)-bis(hydroxymethyl) O,O′-(2-hydroxypropane-1,3-diyl) difumarate. 15.The method of claim 1, wherein the alpha-hydroxy alkyl ester compriseshydroxymethyl 6-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)hexanoate.